The present invention relates to linear motors, which may be configured as an electric synchronous motor or asynchronous motor. Such linear motors find increasingly application in the machine tool construction.
DE 195 47 686 A1 discloses, for example, an electric synchronous linear motor. A secondary part is comprised of several identical secondary individual parts and mounted in a machine bed between two guide rails. Mounted on the latter for guidance is a bridge-like machine carriage having an underside in confronting disposition to the secondary part of the linear motor for support of the primary part. The primary part includes a block for accommodation of electric coils and lines. All existing secondary individual parts have identical configuration as far as the magnetic pole arrangement is concerned and have each four permanent magnets. As viewed in lengthwise direction of the secondary part, a north pole is followed continuously by a south pole, and vice versa. The step width of the pole grid is equal to half the length of a secondary individual part.
Such linear motor may have travel speeds of up to 100 m/min. However, the forces transmittable in travel direction are limited.
It is thus an object of the present invention to provide a linear motor to obviate this drawback.
This object is attained in accordance with the invention by a linear motor which includes a secondary part having several permanent magnets, disposed behind one another with alternating orientation of the polarity, or excitation windings, whereby the permanent magnets or excitation windings are wound helically around a rotation axis, and a primary part having a current-carrying winding disposed in parallel relationship to the permanent magnets or excitation windings and arranged about the rotation axis such that a magnetic traveling field travels helically about the rotation axis.
The force of the traveling field acts along the helical line, and can be split in components which act in axial direction and in circumferential direction. The component acting in axial direction effects a contactless support of the primary part in axial direction by the secondary part. The component acting in circumferential direction effects the establishment of a relative rotation between the secondary part and the primary part about the rotation axis. The speed by which the primary parts and secondary parts move in axial direction relative to one another can, for example, be influenced via the pitch of the wound permanent magnets or excitation windings, i.e. their disposition about the rotation axis.
Further, the pitch can be used to influence the torque effective in circumferential direction between primary part and secondary part. A slight pitch means a higher torque and thus significantly greater forces that can be transmitted in axial direction.
The present invention combines the advantageous characteristics of known linear motors with the advantageous characteristics of ball screw mechanisms known per se.
In most applications, the primary part is the moving part and is designated as rotor. In this case, the secondary part is stationary and designated as stator. As an alternative, the primary part may be stator and the secondary part may be rotor.
According to a further development of the invention, a stator may include a threaded spindle, and the rotor may include a spindle nut, or the rotor may include a threaded spindle and the stator a spindle nut.
Preferably, the winding of the primary part is formed of a plurality of partial windings arranged in series. The pitch of the permanent magnets or the excitation windings of the secondary part is preferably equal to a pitch of the partial windings of the primary part.
The permanent magnets may be provided along several windings about a rotation axis, with permanent magnets of same polarity arranged flush behind one another in parallel relationship to the rotation axis.
The spindle nut is preferably rotatably supported by the threaded spindle via a radial bearing, especially rolling-contact bearing or sliding bearing. This way ensures an accurate positioning of the spindle nut on the threaded spindle.